Computer systems generally utilize auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device (DASD) such as a disk drive incorporating a rotating magnetic disks is commonly used for storing data in magnetic form on the disk surfaces. Data is recorded on concentric, radially spaced tracks on the disk surfaces, and magnetic heads are used to write the data to and read the data from the tracks on the disk surfaces.
Data is written onto a disk by a write head that includes a magnetic yoke having a coil, passing there through. When current flows through the coil, a magnetic flux is induced in the yoke, which causes a magnetic field to fringe out at a write gap. It is this magnetic field that writes data, in the form of magnetic transitions, onto the disk. Currently, such heads are thin film magnetic heads, constructed using material deposition techniques such as sputtering and electroplating, along with photolithographic techniques that include the use of photoresist masks.
Examples of such heads include a first magnetic pole, formed of a material such as NiFe which might be plated onto a substrate after sputter depositing an electrically conductive seed layer. Thereafter a magnetic pedestal could be constructed at a portion of the pole intended as a pole tip and where a write gap is to be formed. The pedestal is generally in the form of a magnetically soft, high magnetic saturation (high Bsat) material, such as CoFe or Ni55Fe45. A high magnetic saturation material is desired because of its ability to concentrate magnetic flux into a small pole tip region for emitting a concentrated magnetic field therefrom. Opposite the pedestal, at a back end of the magnetic pole, a magnetic back gap can be formed. A back gap is the term generally used to describe a magnetic structure that magnetically connects first and second poles to form a completed magnetic yoke as will be described. Although the back gap is constructed of a magnetic material, it need not have as high a magnetic saturation as the pedestal, because it can be constructed to have a much larger cross sectional area. A coil can be formed over the first pole, between the pedestal and the back gap and can be electrically isolated from the pole and yoke by an insulation layer, which could be alumina (Al2O3) or hard baked photoresist. A second pole formed over the first pole completes the magnetic yoke, being magnetically connected with the first pole by the write gap and being magnetically separated from the first pole and the pedestal by a thin layer of non-magnetic material called a write gap.
The write gap material has traditionally been constructed of a thin layer of non-magnetic dielectric material, which has usually been Alumina or SiO2. This thin layer of write gap material is generally deposited as a full film on a planarized surface consisting of the top of the pedestal, the top the coil insulation, the top of the back gap material, and the top of a layer of insulation in the field area.
In order to magnetically connect the second pole with the back gap material, an opening must be created in the write gap material over the back gap. Generally this has been done by spinning on a thin photoresist layer and applying photolithographic techniques to form a photoresist mask that has an opening at the back gap and covers all other areas. A material removal process such as wet etching or ion milling would then be performed to remove the portion of the write gap material over the back gap, exposing the back gap.
Some head designs require the formation of a P2 pedestal in the pole tip area. This P2 pedestal is formed directly over the first pedestal, but on top of the write gap. The two pedestal portions can be self aligned by using the upper P2 pedestal as a mask, and then ion milling to notch into the first pole creating a self aligned pedestal directly under the upper pedestal.
However, since the write gap is generally constructed of a dielectric material such as alumina or SiO2, an electrically conductive seed layer must be deposited prior to plating the upper P2 pedestal. Therefore, in order to form the desired notch in the first pole, the ion mill process must remove not only the desired magnetic material of the first pole, and the non-magnetic material of the write gap, but must also remove the seed layer from the write gap. This requires more extensive ion milling than would be necessary if the seed were not there. An undesirable byproduct of the ion mill process is that in addition to removing the desired write gap and lower pole material, it also undesirably consumes the upper pole pedestal. Therefore, the more extensive the ion mill is the more the upper pole pedestal will be consumed. The additional milling required to remove the seed layer, also means that additional upper pole material must be removed.
The presence of a seed layer on the write gap also degrades magnetic performance. In a most preferred arrangement, a magnetically soft high magnetic moment, high saturation (high Bsat) material would occupy the space closest to the write gap in the pole tip region. This is because this is the region where magnetic flux is most desirably concentrated in order to generate the strongest possible magnetic field at the write gap. However, the seed layer deposited on the write gap is not the most desirable, magnetically soft, high moment, high Bsat material, but is by necessity the material closest to the write gap. Therefore, the most desirable material (that which is plated over the seed layer) gets pushed up to a less desirable location.
Therefore, eliminating the need for a seed layer over the write gap would provide several advantages. One way to eliminate the need for such a seed would be to make use an electrically conductive write gap, such as a metal write gap. One possible material could be for example Rh. However, the use of such metallic write gap materials presents its own challenges. For example, the material removal process needed to remove the metal write gap material over the back gap area might be corrosive to the magnetic back gap material. Furthermore, once the back gap has been exposed, the large surface area of the metal write gap material combined with the much smaller area of the back gap creates a severe electrolytic reaction, with the back gap essentially becoming a sacrificial anode. When exposed to the plating bath during plating of the second pole, the back gap becomes severely corroded and full of voids. The voids in the back gap can even trap plating solution which can continue the corrosion even in the completed head leading to in situ failure of the head.
Therefore, there remains a strong felt need for a manufacturing process that will allow the use of a conductive metal write gap that will address the corrosion issues typically associated with such a metal write gaps. Such a method would preferably utilize existing manufacturing techniques and not result in inordinate extra manufacturing processes.